1. Field of the Invention
This invention relates to ground anchors, more specifically to pivoting ground anchors.
2. General Background
Ground anchors or earth anchors of the pivoting or tilting type are well known and generally include a main body portion having a leading edge adapted to be forced into the ground, a trailing edge including an outturned lip and a cable or guide wire attachment point intermediate the leading and trailing edges generally positioned from about the mid point of the overall length of the anchor or towards the trailing edge so that upon exerting a force on the cable or attached guide wire after insertion of the anchor into the ground, the trailing edge outturned lip will bite into the earth causing the anchor to rotate or pivot to a locked position generally at a right angle to the withdrawal force. Such anchors have included plate anchors such as shown in U.S. Pat. No. 3,969,854, which are generally difficult to drive into the ground. Those anchors have more recently been replaced with cylindrical or tubular shaped anchors having a bore in the body into which a drive rod can be inserted from the trailing edge to a rod abutment point at or adjacent the bottom or end of the bore. Such anchors, as shown in U.S. Pat. No. 4,044,513, employ outturned lips at the trailing edge generally defining an opening into the interior. Such anchors are also shown in U.S. Pat. No. 4,096,673, both of which are assigned to the assignee of this application. Anchors of that type have been sold by the assignee, Foresight Industries, Inc., under the trademark Duckbill and generally consist of cast cylindrical bodies having a cruciform shaped leading edge, a trailing edge with an outturned lip, a blind bore, and a raised rib at a top side remote from the outturned lip, which has an opening therethrough for receipt of either a shackle, a cable, or another load applying device to initiate rotation and “load locking,” i.e. fixing, of the anchor after it is driven into the ground by a drive rod, by means of a hammer, jackhammer, hydraulic press, or the like. Variations on the general shape of such anchors are shown, for example, in U.S. Pat. No. 5,775,037, where the main body may be provided with side edges extending outwardly to the side of the central bore beyond the raised rib. A further variant, shown for example in U.S. Pat. No. 4,802,317, assigned to the instant assignee, utilizes widespread side wings extending laterally of the cylindrical center body portion containing the blind bore. Those lateral wings may have sharpened leading edges and when the anchor is rotated to the locked position the wings increase the contact area between the anchor and the ground providing a wider surface to resist withdrawal of the anchor. Such ground anchors are sometimes referred to as wing anchors. However, the presence of the wings can, in certain instances, can be disadvantageous in that: (a) they provide a much larger area which must be pushed through the ground during insertion of the anchor thereby requiring a higher driving force; and (b) due to their rather large lateral extent with respect to the central body, the force necessary to pivot and lock the anchor is considerably increased. Additionally, (c) the wings can cause a deflection of the anchor during driving. Engagement of an outer reach of the wing with a more drive resistant structure, either a hardened soil structure such as hardened clay or with a stone or rock can have the effect of pivoting the anchor during its driving, which can cause the anchor to change direction as it is being driven into the ground. This can not only result in a mispositioned anchor, it can cause a bending of the drive rod, and in extreme conditions can prevent or hinder withdrawal of the drive rod after the anchor has been placed.
One approach to increasing the straight line drivability of the winged anchors and reducing the driving force necessary is illustrated in U.S. Pat. No. 6,237,289 where the leading edges of the wings are provided with a series of separate chisel leading edges that are stepped back one from another axially and extend for short distances radially thereby providing the leading edges of the wings with a series of separate leading edges that are each longitudinally offset with respect to one another and radially offset with respect to the main body. While this serration or stepping of the leading edges of large wing anchors is an improvement over prior large wing anchors, the necessity for a higher driving force and the difficulties associated with rotation to the locked position remain a problem. Such anchors are therefore used generally only where high load resistance is required, and the more cylindrical anchors are used where lower resistance load levels are anticipated.
The use, however, of cylindrical anchors, with their cruciform driving edges leaves the anchor, during driving, at risk of wandering or deviating from a straight path. Since such anchors are normally driven into the ground at an angle to the vertical, which will represent the angle of the application of load after setting of the anchor, and since the load application is generally at an angle other than 90 degrees, particularly where the anchor is used to anchor a guide wire, a fence end or tree support or the like, it is sometimes difficult to drive the anchor straight. Substantially cylindrical anchors generally have less holding or load bearing capabilities than similar sized winged anchors but are easier to drive and to rotate to a locked position.
It would therefore be an improvement in the art if generally cylindrical ground anchors could be provided with a reduced driving resistance, with a better straight path driving tendency and with improved load bearing capabilities.